AlphaComplexDQPException

Thrown when the inner QP fails to converge. In practice this means a genuinely near-degenerate configuration (see the rankTolerance doc on AlphaDQPSettings and WORKLOG.md at the repo root for the full derivation) -- not simply "too tight a tolerance", since no fixed tolerance safely eliminates every such case. Loosening AlphaDQPSettings may help but isn't guaranteed to; AlphaComplexDQPBuilder.solveAtVertex already catches this per-candidate (excluding just that candidate, logged to stderr) so it should only reach a caller from a direct DualQP.solve call.